In many cities the utilities are located beneath the surface of the earth, usually beneath the surface of the streets. These utilities are usually placed in tunnels or conduits. In the older cities, such as New York City, these utilities have been located in these tunnels or conduits for many years/decades. Over time, the conduits which carry these utilities wear out and break. For example, water main breaks are a well known example of a utility conduit failing. Another serious problem is the failure of electrical transmission lines in conduits and tunnels. These failures usually result in fires which must be quickly extinguished to prevent further damage.
While it is desirable to replace very old utilities in conduits and tunnels, it is not always practical. Recently, a new tunnel for the supply of water was built under New York City. This was a tremendous project which took many years to complete and was very expensive. The replacement of the electrical transmission lines under the streets of New York City should also occur. However, due to financial restraints and other limitations, these electrical transmission lines have not been replaced. Thus, these old electrical transmission lines break down or fail which results in electrical fires. These fires are commonly seen as smoke coming from manhole covers in the streets and sidewalks of a city. It has been estimated by Consolidated Edison that there are approximately 40 electrical fires per day under the streets of New York City.
The cost of repairing and replacing the electrical transmission lines damaged by these fires is approximately $100,000.00 per linear foot of transmission line. Therefore, it is imperative that these fires be extinguished as quickly as possible. Normally, when there is a fire, the firefighters locate the fire and call the utility to cut off the electrical power to that section of the electrical transmission line so that the fire can be extinguished with water. Because of the large voltage and current sent through these transmission lines, the application of water to these lines without the power being turned off would result in the instant electrocution of the firefighter. Accordingly, the firefighters wait until there is no doubt that all the electrical power has been turned off in the transmission lines they are about to extinguish. This, of course, results in the fire burning for an unnecessary extra amount of time and having the utility incur an unnecessary financial expense.
Once it has been established that the electrical power has been turned off, the firefighters enter the underground tunnel or conduit through a manhole and apply large amounts of water onto the electrical transmission lines which are on fire and/or smoldering until they determine that the fire has been completely extinguished and will not flare-up or restart. This large amount of water usually results in the destruction of good electrical transmission lines that are not involved in the fire. The water also fails to suppress the toxic gases produced by the burning electrical insulation, wires, and electrical components.
After the fire has been extinguished, the area must be cleaned up and the residue from the fire removed. Normally, a clean-up crew enters the tunnel or conduit to vacuum up the water, particulate ash from the burnt components and other residue produced by the fire. This is a costly operation. Finally, after the clean-up crew has completed its job, a crew of electricians enters the tunnel or conduit to replace the electrical transmission lines and other equipment which has been destroyed/damaged by the fire with new equipment/components.